Lunar Orbiter 1

NSSDC/COSPAR ID: 1966-073A

Description

The Lunar Orbiter 1 spacecraft was designed primarily to photograph smooth areas of the lunar surface for selection and verification of safe landing sites for the Surveyor and Apollo missions. It was also equipped to
collect selenodetic, radiation intensity, and micrometeoroid impact data.
The spacecraft was placed in an Earth parking orbit on 10 August 1966 at
19:31 UT and injected into a cislunar trajectory at 20:04 UT. The
spacecraft experienced a temporary failure of the Canopus star tracker
(probably due to stray sunlight) and overheating during its cruise to the
Moon. The star tracker problem was resolved by navigating using the Moon
as a reference and the overheating was abated by orienting the spacecraft
36 degrees off-Sun to lower the temperature.

Lunar Orbiter 1 was injected into an elliptical near-equatorial lunar
orbit 92.1 hours after launch. The initial orbit was 189.1 km x 1866.8 km
and had a period of 3 hours 37 minutes and an inclination of 12.2 degrees.
On 21 August perilune was dropped to 58 km and on 25 August to 40.5 km.
The spacecraft acquired photographic data from August 18 to 29, 1966, and
readout occurred through September 14, 1966. A total of 42 high resolution
and 187 medium resolution frames were taken and transmitted to Earth
covering over 5 milliom square km of the Moon's surface, accomplishing
about 75% of the intended mission, although a number of the early high-res
photos showed severe smearing. It also took the first two pictures of
the Earth ever from the distance of the Moon. Accurate data were acquired
from all other experiments throughout the mission. Orbit tracking showed
a slight "pear-shape" to the Moon based on the gravity field and no
micrometeorite impacts were detected. The spacecraft was
tracked until it impacted the lunar surface on command at approximately 6.70 degrees N
latitude, 162 degrees E longitude on the Moon's
far side on October 29, 1966 at 13:30 UT on its 577th orbit. The early end to the nominal one year mission was due to the small amount of remaining attitude control gas and other deteriorating conditions and was planned to avoid transmission interference with Lunar Orbiter 2.

Spacecraft and Subsystems

The main bus of the Lunar Orbiter had the general shape of a truncated cone, 1.65 meters tall and 1.5 meters in diameter at the base. The spacecraft was comprised of three decks supported by trusses and an arch. The equipment deck at the base of the craft held the battery, transponder, flight progammer, inertial reference unit (IRU), Canopus star tracker, command decoder, multiplex encoder, traveling wave tube amplifier (TWTA), and the photographic system. Four solar panels were mounted to extend out from this deck with a total span across of 3.72 meters. Also extending out from the base of the spacecraft were a high gain antenna on a 1.32 meter boom and a low gain antenna on a 2.08 meter boom. Above the equipment deck, the
middle deck held the velocity control engine, propellant, oxidizer and
pressurization tanks, Sun sensors, and micrometeoroid detectors. The third
deck consisted of a heat shield to protect the spacecraft from the firing of
the velocity control engine. The nozzle of the engine protruded through
the center of the shield. Mounted on the perimeter of the top deck were
four attitude control thrusters.

Power of 375 W was provided by the four solar arrays containing 10,856 n/p solar cells which would directly run the spacecraft and also charge the
12 amp-hr nickel-cadmium battery. The batteries were used during brief
periods of occultation when no solar power was available. Propulsion for
major maneuvers was provided by the gimballed velocity control engine, a
hypergolic 100-pound-thrust Marquardt rocket motor. Three-axis
stabilization and attitude control were provided by four one-lb nitrogen
gas jets. Navigational knowledge was provided by five Sun sensors, Canopus
star sensor, and the IRU equipped with internal gyros. Communications were
via a 10 W transmitter and the directional 1 meter diameter high gain
antenna for transmission of photographs and a 0.5 W transmitter and
omnidirectional low gain antenna for other communications. Both antennas
operated in S-band at 2295 MHz. Thermal control was maintained by a
multilayer aluminized mylar and dacron thermal blanket which enshrouded the
main bus, special paint, insulation, and small heaters.

Results of the Lunar Orbiter Program

The Lunar Orbiter program consisted of 5 Lunar Orbiters which returned photography of 99% of the surface of the Moon (near and far side) with resolution down to 1 meter. Altogether the Orbiters returned 2180 high resolution and 882 medium resolution frames. The micrometeoroid experiments recorded 22 impacts showing the average micrometeoroid flux near the Moon
was about two orders of magnitude greater than in interplanetary space but slightly less than the near Earth environment. The radiation experiments confirmed that the design of Apollo hardware would protect the astronauts from average and greater-than-average short term exposure to solar particle events. The use of Lunar Orbiters for tracking to evaluate the Manned Space Flight Network tracking stations and Apollo Orbit Determination Program was successful, with three Lunar Orbiters (2, 3, and 5) being tracked simultaneously from August to October 1967. The Lunar Orbiters were all eventually commanded to crash on the Moon before their attitude control gas ran out so they would not present navigational or communications hazards to later Apollo flights. The Lunar Orbiter program was managed by NASA
Langley Research Center and involved building and launching 5 spacecraft to the Moon at a total cost of $163 million.